A Mathematical model of the HIV infected human immune system is presented. The model consists of a system of ordinary differential equations for the populations of uninfected CD4+T cells, infected CD4+T cells and free virus in the blood. The model is constructed, and parameters chosen, so that turnover rates and life spans for these populations agree with clinical data. The model is used to simulate chemotherapy treatment of HIV infection. The simulations are based upon preliminary clinical reports of treatment with combinations of antiviral drugs involving standard reverse transcriptase inhibitors and newly developed protease inhibitors. The models incorporate the apperance of drug-resistant viral strains, which is the key limiting factor in the effectiveness of HIV Chemotherapy. The simulations focus upon the timing of treatment initiation.